In a fifth generation system which is considered as a further development of the wireless communication system, the use of a small-cell to reduce a communication area will be inevitable as a measure to further enhance throughput and frequency usage efficiency.
If the small-cell is introduced, the number of small-cell is increased dramatically so that the small-cells exist all over the city, and installing a cable line (such as an optical line) for connecting all small-cell base station (a relay station) to a backhaul is difficult in view of cost and construction. Accordingly, it has been studied that wireless is used as a line for connecting a small-cell base station to a backhaul. As a specific example, a large-cell base station and a small-cell base station are connected wirelessly.
The use of wireless for such a backhaul is not limited to areas such as isolated islands or sparsely populated areas that a wired communication is not available and will be extended to urban areas or the like in order to reduce a installation cost of the wiring (for example, see JP-A-2014-216758).
Since the laying of wires for connecting the network is not required, it is possible to add more small-cells with a degree of freedom.
Meanwhile, in order to perform wireless communication between a remote wired line side portion and a small-cell base station (a relay station), a dedicated wireless device is mainly used in the background device for realizing a wireless backhaul system.